In the medical field, various types of body implantable leads are known and used. One type of commonly used implantable lead is an endocardial pacing lead.
Endocardial pacing leads are attached at their proximal end to an implantable pulse generator and at their distal end to the endocardium of a cardiac chamber. The distal end of an endocardial lead may engage the endocardium by either an active fixation mechanism or a passive fixation mechanism.
Active fixation mechanisms use a structure, such as helix or hook, to physically engage into or actively affix themselves onto the heart. Passive fixation mechanisms, such as a tine assembly, lodge or passively fix themselves to the heart.
A preferred means for introducing an endocardial lead into the heart is through a vein. During the implantation of an transvenous endocardial lead body, the lead may be introduced into the heart using either the subclavian or cephalic vein in the shoulder area under the pectoral muscle.
To anchor the lead body at the venous entry site, the lead body is secured to an anchoring sleeve, the anchoring sleeve, in turn, is secured to the surrounding fascia or tissue. Generally the lead body is secured to an anchoring sleeve through a series of circumferential sutures wrapped around the anchoring sleeve to thereby squeeze or compress the sleeve to the lead. The sleeve itself is additionally secured to the surrounding fascia or tissue through further sutures.
Anchoring sleeves in present use are generally tubular structures molded out of a soft, implantable elastomer such as silicone. Such sleeves may be implanted as follows: First, the anchoring sleeve is slid along the lead body to the location at which the lead is to be anchored to the underlying tissue. One or more sutures are then tied around the sleeve to compress it and thereby secure it to the lead body. Circumferential grooves in the outer surface of the sleeve are typically provided for this purpose. The last step is to anchor the sleeve to adjacent body tissue; sutures may be passed through a pair of tabs projecting from the sleeve to provide the required anchoring.
This type of common design has evolved due to the conflicting performance criteria anchoring sleeves generally have. First, because not all patients are the same size and not all doctors introduce the lead into the vein at exactly the same site relative in distance to the heart, it is necessary for the anchoring sleeve to be able to be slid or moved along the lead body to permit it to be properly located along the lead prior to being secured thereto.
Although anchoring sleeves must be able to be slid along a lead body, they must also be able to be securely attached to the lead body. To date a preferred method of attaching or affixing the sleeve and lead body together is by frictionally engaging the lead body and sleeve. Typical anchoring sleeves are frictionally attached to a lead body through sutures tightly wrapped about the sleeve in conjunction with the use of a material for the sleeve which has a relative high coefficient of friction against the lead body. U.S. Pat. No. 4,553,961 to Pohndorf et al., for example, discloses an anchoring sleeve featuring a gripping enhancing structure to facilitate gripping of the lead body. One drawback to such a design is that the gripping structure may be a second part, thereby complicating manufacturing and increasing cost. A more serious drawback with such a design is that the gripping structure often unintentionally engages and thus locks to the lead body, such as when a physician grasps the anchoring sleeve and simply tries to position it along the lead body.
Because anchoring sleeves typically are difficult to slid along the lead body, they have often been made having a larger diameter central lumen or throughbore (i.e. bore in the sleeve through which the lead body passes) than the lead body. That solution, however, itself created performance difficulties. Namely because the sleeve has a larger inner diameter than the outer diameter of the lead body, it was made difficult to sufficiently compress or squeeze the sleeve so as to grip about the lead body.
In order to permit the sleeve to be sufficiently compressed or squeezed through sutures, sleeves have often featured slots or slits across the sleeve. U.S. Pat. No. 4,516,584 to Garcia, for example, discloses the use of four slits located between the suture grooves. These slits permitted the sleeve to be squeezed by the sutures and thereby securely frictionally engage the lead body.
One drawback to the design of Garcia, however, is that the slits go only between the suture grooves, thereby providing only a limited ability to be squeezed against the lead body. U.S. Pat. No. 5,129,405 to Milijasevic et al. apparently attempted to solve this drawback of Garcia by providing a slit entirely across the length of the sleeve, including completely across the suture grooves. Through such a design, it appears the lead may be squeezed in the area not only between the grooves, but also in the area outside the grooves and across the entire length of the sleeve.
One serious drawback with the design of Milijasevic et al. is that the sleeve may be readily squeezed against the lead body by simple handling. That is, when the physician grasp the sleeve in an effort to properly position it along the lead body, even minor pressure from the doctor's fingertips may cause the sleeve to frictionally engage the lead body, thereby greatly inhibiting its ability to be moved to the proper location.